This invention relates generally to the forming of metal parts and particularly to the in press adjustment of the workpiece holding force in accordance with the thickness of the workpiece.
The quality of parts made by forming thin sheets of metal, such as the parts for the electron gun of a color television kinescope, is highly dependent upon the thickness of the material from which the parts are formed. Deviation in the metal thickness from the nominal value results in changes of the required forming force and pressure pad holding force. These variations in forces produce parts for which the bending, spring back and wall thinning is very difficult to predict and compensate. Additionally, changes in the forming forces contribute to excessive wear and fatigue of the dies from which the parts are formed, and thus substantially reduce the life of the dies.
Currently, the metal forming industry measures the thickness of the stock based upon a discrete quality control scheme in which samples from lots are selected and the thickness of the samples measured. Typically, the samples are selected from the ends of the roll and therefore the sample measurements are not necessarily indicative of the thickness of the metal in the middle of the roll. For these reasons, the pressure pad holding forces can be either excessive or deficient because the sample thicknesses are used to calculate the holding forces. Accordingly, there is a need for a system for automatically optimizing the pressure pad holding force in accordance with the actual thickness of the workpiece. The instant invention fulfills this long felt need.